Density of States and the Role of Energetic Disorder in Charge Transport in an Organic Radical Polymer in the Solid State

On the basis of atomistic simulations of the stable organic radical polymer material poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA), various material properties relating to charge transport were evaluated in terms of the Marcus charge-transfer rates between radical sites. The reorganization energy of the PTMA monomer unit was calculated using density functional theory to provide an approximate value to enter into the Marcus charge-transfer rate. The role of energetic disorder in the charge transfer between sites caused by the different local environments seen by radical sites is examined in terms of both steric and electrostatic effects. The electronic coupling between sites was examined in terms of the intersite network, morphological features, and energetic disorder. Energetic disorder was found to result in both sites that act as traps and paired sites that were highly coupled to each other and would act as a single site for transport purposes.